1. Field of the Invention
The present invention concerns a porous implant material for inducing the growth of bone or other hard tissue into the pores of the implant material, and relates also to a method for producing such material.
2. Background of the Related Art
In the healing arts there is often a need for an implant material to replace, repair, or reconstruct hard tissue in the body of a patient. For example, hard-tissue implant materials are used in medicine and veterinary medicine as a prosthetic bone material to repair injured or diseased bone. Hard tissue implant materials are also used in the construction of prosthetic joints and to fix prosthetic joints to bone. In dentistry, hard tissue implant materials are used in the construction of prosthetic teeth and tooth roots and to replace or augment the edentulous ridge.
U.S. Pat. Nos. 4,535,485 and 4,536,158 disclose certain implantable porous prostheses for use as bone or other hard tissue replacement which are comprised of polymeric materials. The prostheses of these references are composed generally of polymeric particles. The particles have an inner core comprised of a first biologically-compatible polymeric material such as polymethylmethacrylate and an outer coating comprised of a second biologically-compatible polymeric material which is hydrophilic, such as polymeric hydroxyethylmethacrylate. The particles may incorporate a ratio-opaque material to render the particle visible in an X-ray radiograph. The particles may be bonded together to form a unitary structure which can be implanted in the body. Alternatively, a mass of the particles may be implanted in the body in an unbonded, granular form. In either the bonded or the unbonded form, interstices between the implanted particles form pores into which tissue can grow. Thus, the bioabsorbable particles serve as a structural support and guiding matrix for encroaching bone deposits derived ultimately from adjacent fresh bone. The hydrophilic coating on the particles facilitates infusion of body fluids into the pores of the implant, which facilitates the ingrowth of tissue into the pores of the implant.
U.S. Pat. No. 4,728,570 discloses a calcium hydroxide treated polymeric implant material. The polymeric material disclosed therein is polymethylmethacrylate (PMMA) having a coating of polyhydroxyethylmethacrylate (PHEMA). Calcium hydroxide is distributed in the mass of polymeric particles to induce the growth of hard tissue.